outlines; diglaction, 1, 2, - ERIC - Education Resources ... · PDF fileAssign worksheet (10 min)- ... Digestion Control Factors - Food #7. Quality of Food. Should be 5-8% solids

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Carnegie, John W., Ed.An,crobic Digestion. Instructor's Guide. BiologicalTreatment Process Control.Linn-Benton Community Coll., Albany, Oreg.Environmental Protection agency, Washington, DC.Office of Drinking Water.84EPA-T90123864p.; For related documents, see SE 045 333-354.Linn-Benton Community College, 6500 S.W. PacificBlvd., Albany, OR 97321 (Instructor's guide andaccompanying slides).Guides - Classroom Use Guides (For Teachers) (052)

MF01 Plus Postage. PC Not Available from EDRS.ler,ielogy; Laboratory Procedures; Post SecondaryEducation; *Sludge; *Training methods; *WasteDisposal; *Waste Water; *Water Treatment*Anaerobic Digestion; Unit Processes

ABSTRACTThis instructor's guide contains materials needed to

teach a four-lesson unit on anaerobic digestion control. Thesematerials include: (1) unit overview; (2) lesson plans; (3) lecture

.outlines; (4) student worksheets for each lesson (with answers); and(5) two copies of a final quiz (with and without answers). Lesson 1is a review of the theory of anaerobic digestion. Topics coveredinclude the nature of raw sludge, purposes of anaerobic diglaction,

the biological process, and the results of digestion. Lesson 2 coversclassification of digesters and system components. Classification on

the is of function and structure is discussed. The components of

the mi.ing, heating, and gas system are also covered. Lesson 3 dealswith process control. The factors which affect operation, controlparameters, and sampling and testing are addressed. Lesson 4 is onmathematics calculations relating to process control. Lessons 1, 2,

and 3 are supported by a set of 35mm slides (which are indicated inthe lecture outlines for these lessons). (JN)

************************************************************************ Reproductions supplied by EARS are the best that can be made *

* from the original document. *

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U.S. DEPARTMENT OF EDUCATIONNATIONAL INSTITUTE OF EDUCATION

El UCATIONAL RESOURCES INFORMATIONCENTER IERICI

This document has been reproduced asloLeived 11010 the persmi or organization

OfIgif Idling itMinor changes have been rn,de to improve

reproduction quality

Points of view or opinions sated in this (locomeat do not necessarily represent official NIT

position of policy

"PERMISSION TO REPRODUCE THISMATERIAL IN MICROFICHE ONLYHAS BEEN GRANTED BY

ahn to. eamegle.

TO THE EDUCATIONAL RESOURCESINFORMATION CENTER (ERIC)."

BIOLOGICAL PROCESS TREATMENT CONTROL

ANAEROBIC DIGESTION

Instructor's Guide

Outline Developed By:E.E. "Skeet" Arasmith

Linn-Benton Community CollegeAlbany, Oregon

Edited By:John W. Carnegie, Ph.D.

Linn-Benton Community CollegeAlbany, Oregon

Instructional Design By:Priscilla Hardin, Ph.D.

Priscilla Hardin Instructional ServicesCorvallis, Oregon

Developed Under:EPA Grant #1901238

1984

:3

ANAEROBIC DIGESTION

Instructor's Guide411110b

Table of Contents Page #

Overview of Lessons I-AND-1

Lesson Plans I-AND-1

Lecture Outlines

Lesson I - Process Theory I-AND-3

Lesson II - Types and Components I-AND-7

Lesson III - Process Control I-AND-10

Lesson IV - Calculations I-AND-15

Overhead Masters I-AND-17

Answers to Worksheets I-AND-26

Final Quiz I-AND-37

Answers to Final Quiz I-AND-47

ANAEROBIC DIGUTION

Overview

This unit on anaerobic digestion process control is divided into four

lessons. Lesson 1 is a review of the theory of anaerobic digesticn. Topics

covered include the nature of raw sludge, purposes (.7 anaerobic digestion,

the biological process, and the results of digestion. Lesson 2 covers

classification of digIsters and system components. Classification on the

basis of function and structure is discussed. The components of the mixing,

heating, and gas systems are well covered. Lesson 3 deals with process

control. The factors which affect operation, control parameters, and sampling

and testing are addressee. Lesson 4 is on math calculations relating to

process control.

Lessons 1, 2 and 3 are supported by 35 mm slides. Most of these slides

were developed by LBCC for use in EPA Course #166, Solids Handling and

Treatment. They are used in this unit in a different order and with expanded

written material. The Course #166 slide/tape program and written material on

Anaerobic Digestion can be obtained from:

Water/Wastewater DepartmentLinn-Benton Community Colleg&.6500 ()W Pacific Blvd.Albany, OR 97321

(503) 928-3620

The text in the student manual is excerpted from EPA Manual 430/9-76-001,

"Operations Manual; Anaerobic Sludge Digestion," EPA-IRC, Ohio State Univ.,

Columbus, OH, 1976.

Lesson Plans

Lesson 1 - Process Theory

- Assign text Sec. 1 "Anaerobic Sludge Digestion"ahead of time if possible

- Lecture using slides (30 m1r)

- Assign worksheet (10 min)

- Correct and discuss worksheet (15 min)

I-AND-1r-

Lesson 2 - Types and Components

- Assign text Sec. 1 "Anaerobic Sludge Digestion"ahead of time, if possible (if not already assigned

above).

- Lecture using slides (30 mir)


- Col rect and discuss worksheet (15 min)

Lesson 3 - Process Control

- Assign text Sec. 2 "Digested Process Control" aheadof time, if possible

- Lecture using slides (45 min)



Lesson 4 - Calculations

- Refer students to portions in text which discuss

. calculations. Portions are spread throughout the

first and second sections.

- Explain calculations and work example problem.Use overheads of formulas provided. (30 min)



- Assign final quiz (20 min)

Additional suggestions

- Obtain samples of raw and digested sludge. Samples of

well avd poorly digested sludge would be valuable.

- Display examples of gas safety and control equipment;flame traps, heat sensitive valves, meters, manometers,etc.

Lesson I - Process Theory

Slide #

#1 & #2

#3

#4

ANAEROBIC DIGESTION

Lecture nutline

Title & Credit Slide

Functions of Anaerobic Digestion

5 Main Functions:

- Stabilizes volatile matter40-60% reduction

- Reduces mass and/or volume ofsludge

- Reduces offensive odor

- Reduces number of pathogenicorganisms

- Conditions sludge - changesnature of sludge to make itmore readily dewaterable

Results - Usable By-products

Methane gas

Digested sludge

- Supernatant which mustbe recirculated throughplant

Nature of Sludge Fed to Digester

#5 Raw - Primary Clarifier

#6 2-5% solids

#7 60-80% volatile

#8 Volatility depends on age andnature

#9 Biological - Waste Activated Sludge

- Organic

#10

#11

Chemical - Inorganic precipitates

- Pho ,horus removal

Pv:mary clarifier solids are the mostcommon type digested anaerobically

fypes of Digestion

Anaerobic

Advantages - useful gas produced

- effective treatment

- low operating cost

Disadvantages - slow digestion

- upset easily bysudden changes

#12 Aerobic

Advantages - treat WAS better

- treat high water content(thin) sludge better

- inexpensive to construct

Disadvantages - high operating cost -air

- no useful by-products

The Digestion Procesf

Partially digest...d sludge subjected tofurther digestion - by anaerobic bacteria

#13 Two Stages

#14 Acid Formers

Convert absorbed organics (V.S.)into volatile acids (50-300 mg/L)

Mostly acetic acid

#15 Methane Formers

I-AND-4

S

Use volatile acids as food

Produce CO2'

CH4, H2O &

alkalinity

#16 Alkalinity (1500-3000 mg/L)

Buffers & neutralizes

Strict anaerobes

Results of Digestion

#17 Reduced (stabil'zed volatile solids)40-60% less V.S.

Inert (nonvolatile) solids are not

touched

#18 Gas and useful sludge produced

Supernatant high in SS and BOD mustbe treated

#19

#20

The Digester Zones

Gas, Scum, Supernatant, Sludge

Gas

/01 Methane CH4

Carbon dioxide CO2

Moisture & minor gases (H2S, N2)

65-70% CH4

#22 12-18 ft3

gas/lb V.S. digested

#23 600-800 BTU's/ft3

Commercial gas 1000-1100 BTU's/ft3

Gas System

#^.4 Collects gas for heating, mixIng,or wasting

#25 Uses of Surplus Gas

#26, #27, #28 Heating digester & buildings

Heat exchange

#29 Fueling engines & blowers,generators

#30 Mixing

#31 Explosive nature of gas

Explosive range air to methane20:1 to 5:1

Corrosive - CO2creates carbolic acid

I-AND-5

9

#32 Scum

#33 More prodnent in unmixed tanks

Caused by uplift of gas

Tend to reduce mixing

Concentrates food

5-15 feet thick

Contains - petroleum products

- rubber material

plastics

- cigarette filter tips

- hair

- grit

#34 Supernatant

#35

Two sources - carrier water

- disrupted (dead)bacterial cells

High BOD - 1000-10,000 mg/L

High SS 5000-15,000 mg/L

Can cause severe loading viasidestream to headworks

Supernatant depends on type of feedsludge

Good settling critical

#36 Active Sludge Zone

#37

#38

#39

Good sludge - black, no green orgray streaks

- dewaters easily

- no noxious odors

- 40-60% lower V.S.than feed

Digested sludge can be disposedof by land application, landfillor incineration (less common)

#40 Summary and Review

I-AND-6

10

ANAEROBIC DIGESTION

Lecture Outline

Lesson II - Types and Components

Slide #

#1 & #2 Title & Credit Slides

Two Major Types

#3 Old, open top, unmixed

Imhoff Tanks

#4 Covered tanks with mixing

Classification of Digesters

#5 Function

#6 Primary Digester

Site of most of the digestion

#7 Secondary and Gas Holding

Serves as storage for sludgeand gas

#11

Roof Design

Fixed Roof Design

Roof - steel, concrete

Internal pressure 8" of water

Must control gas removal andliquid level

#12, #13, #14 Floating Roof Design

#16

Volume can fluctuate, emptyperiodically

Roof rides on liquid and gas

Corbels stop roof from going toofar down

Internal pressure 8-11" of water

Usually used as secondary digesters

#17, #18

#19

Gas Holding Roof Design

Used for gas storage

Roof floa4J on gas pressure

#20 Temperature

#21

Psychrophilic

Mesophilic

Thermophilic

Components

Commercial gas storage

On hand for emergency aidstart-up use

Cannot store digester gas

Heat Exchangers

Internal

#22, #23 Steam injection

#24 Internal heat exchangers

#25, #26

#27 - #33

#34

Direct as - extremely dang'rous

External

Uses methane fueled lers

and heat exchangers

Mixing

Gas

Mechanical

Combination

#35 Gas System Components

#36 Flame Arrestors

#37 Heat Sensitive Valve

#38 Pressure Valves

#39 Moisture & Sediment Traps

#40 Manometer

#41 Gas Meter

#42 Wasting Burners

I-AND-8

12

#43, #44 Sludge Pumps

Piston Pumps

Progressive Cavity

I-AND-9

1;3

ANAEROBIC DIGESTION

Lecture Outline

Lesson III - Operational Control

Slide #

#1 & #2

#3

Title & Credit Slides

Digestion Control Factors - Outline slide

#4 Digestion Control Factors - Bacteria

#5 Seed Sludge

Need 20 times more seed than foodby wt. of volatile matter

Acid formers are facultativeanaerobes present in wastewatersludge

Methane formers - strict anaerobestakes time to develop population

#6 Digestion Control Factors - Food

#7 Quality of Food

Should be 5-8% solids

Non-toxic

StahlP pH

Feed at a steady rate & frequency

Keep excess water at a minimum

Sludge usually less dense at night

Quality. not quantity is important

Remove grit and grease

Typical sludge concentrations

Primary Raw 5-8%

WAS 1.5-2%

T.F. 1-3%

Mixed Primary/A.S. 3-5%

#8

#9

#10

#11

#12

#13

#14

Digestion Control Factors Loading

Load on basis of V.S./ft3(FM)

0.03-0.1 lbs/ft3

Load on basis of V.S. feed/V.S. it

digester

1:20

Hydraulic loading

Affects detention time

Maintain good buffering by controllingwithdrawal

Maintain buffering by recycling frombottom of secondary 50% of raw feed/day

Digestion Control Factors - Mixing

Organisms must come in contact with food

Types of Mixing

Natural - Gas

- Loading of sludge

Artificial Gas

Mechanical

Combination

Digestion Control Factors - Environment

pH - buffering capacity

Maintain Volatile Acid toAlkalinity Ratio

VA

Alk

Temperature

1-AND-11

15

0.25 or less

Best range 95-98° F

phychrophilic less than 68° F

mesophilic 68-113° F

thermophilic above 113° F

Best temperature established by CO2production at 30% or lower

#15 Vary by not more than 1° F/day

#16

#17 pH

Control temperature for energyefficiency

6.8-7.2 best

6.4-7.4 tolerable

Volatile Acids

50-300 mg/L

Alkalinity

3000-6000 mg/L

#18 Digestion Control Factors - Time

Control detention time by feed,pumping rate and withdrawal rate

Scum Blanket Control

Provide Adequate mixing

Try to less than 24" thick

Supernatant Control

Monitor BOD and SS, keep both lessthan 5000 mg/L

Allow ample settling time, 8-12 hrs

Select and maintain level in digester

#19 Monitoring

Sample poi its

Raw

Supernatant

Gas

Digested Sludge

#20 Digesting Sludge - Thief hole

#21

I-AND-12

Tests

16

Flow

Alkalinity

#22

#23

#24

#25

pH

Volatile Acids

Temperature

% Moisture

Volatile Solids

pH and Temperature

Feed

Supernatant

Digested Sludge

Digesting Sludge

Flow

Feed

Digested Sludge

Digesting Sludge

Total & Vo.latile Solids, % Moisture

Feed

Supernatant

Digested Sludge

Digesting Sludge

CO2

Gas

BOD, Suspended Solids

Supernatant

#26 pH and VA/Alk

Digesting Sludge

Review of Monitoring

Trend Chart Test Data

#27

#28

#29 Safety

I-AND-13

Rubber soled shoes

No open flames, no smoking

Light waste burner cautiously

17

#30 Fix gas leaks immediately

Check for gas in air before enteringempty digester

ANAEROBIC DIGESTION

Lecture Outline

Lesson IV - Calculation

1. Calculate pounds T.S. in Feed or Supernatant per day

T.S., lbs/day = T.S., mg/L X Flow, Mgal/day X 8.34

2. Calculate pounds T.S. in Digester

T.S., lbs = T.S., mg/L X Vol, Mgal X 8.34

3. Calculate Hydraulic Detention Time

D.T., daysVol

'

gal

Feed, gal/day

4. Calculate pounds Volatile Solids in feed per day

V.S., lbs/day = T.S., lbs/day X % Volatility

5. Calculate Volatile Solids Loading in lbs/day/ft3

Loading, lbs/day/ft3 V.S., lbs/day

Dig. Vol, ft3

6. Calculate Volatile Solids Reduction in Percent

outSin - VV.S. . .

V.S. reduction, % X 100%V.S. in - (V.S. in X V.S. out)

7. Calculate pounds of Volatile Solids Digested

V.S. digested, lbs/day/ft3

= Loading, lbs/day/ft3X V.S.

Reduction %

8. Determine pounds of lime to adjust pH

Do bucket test on a small sample

Use ratio to determine pounds for total digester

9. Determine pounds of lime required to neutralize volatile acids

lbs of lime = Dig Vol, Mgal X V.A., mg/L X 8.34

I-AND-15

19

10. Determine pounds of lime required to neutralize ifvolatile acids and alkalinity are known

Usually want 500 mg/L excess alkalinity

Alkalinity is equal to 0.833 times V.A.

Steps to determine

1. Determine alkalinity to neutralize V.A.

Alk = 0.833 X V.A.

2. Subtract alkalinity present

3. Add excess alkalinity (500 mg/L)

4. Ammonia = 2.78 X Dig Vol, Mgal X Alk, mg/L

5. Anhydrous Ammonia usually 80% ammonia

TOTAL SOLIDS'L B S

= T. S ., xV°G/L 1-"MGAL 3'34

2 '2

ai

TOTAL SOLIDS, LBS/DAY= T.S.,mG/L X FLOW,m

X8,34

mGAL/DAY

2,4

2 3

VOLATILE SOLIDS,LBS/DAY

x % VOLATILITYT.S.J LBS/DAY

2:)

DETENTION T IMF"'DAYS

27

VOLJGAL

FEED FLOW,GAL/DAY

LOADING'LBS/DAY/FT3

N

28

V,S,LB DAY

DIG, VOL. 7FT)

V.S. DIGESTED -LOADING

as//DAY/

/FT

23

LBS/DAY/FT3x V.S. REDUCTION,T

30

VOLATILE SOLIDS REDUCTION,? =

31

VISIJOUT

(V.SJIN X V.S.,OUT)

ALKALINITY = 0,833 x VOLATILE ACIDS

32

POUNDS LIME = DIG VOL,MGAL

X VA,,mG/L x 8,54

33

ANAEROBIC DIGESTION

Answers to Worksheet 1 - Process Theory

1. List four purposes of anaerobic digestion of sewage sludge.

a. Stabilize volatile matter

b. Reduce mass and/or volume

c. Reduce odor

d. Reduce pathogens

Condition sludge

2. Raw sludge from a primary clarifier contains 60 to 80 % volatilematter.

3. List one advantage and one disadvantage which anaerobic digestion hasover aerobic digestion.

a. Advantage Useful gas producedEffective treatmentLow operating cost

b. Disadvantage Slow digestionEasily upset

4. The anaerobic sludge digestion process is a two stage process.

5. Volatile solids in raw sludge are attacked by acid forming (anaerobic)

organisms to form volatile (low molecular weight) acids.

6. Methane formers then feed off of the volatile acids to form

CO7 (carbon dioxide) , CH4 (methane) H2O (water)

and alkalinity.

7. Which of the two types of major bacteria involved in the anaerobic digestionprocess is a str.I.A anaerobe?

Methane formers

8. Stabilizing waste by digestion should reduce the volatile content by

40 to 60 %.

9. The gas produced by a digester is mainly 65-70 % methane and 30-35 %

CO2

I-AND-26 3 4

10. 12 to 18 ft3 of gas will be produced for each lb of

volatile solids dige$ted.

11. One ft3 of digester gas will produce 600 to 800 BTU of heat.

12. Name three uses of digester gas:

a. Heating Digesters

b. Heating buildings

c. Fuel for engines, blowers, generators

Mixing

13. Methane can explode when the ratio of air to methane is between 20:1

and 5:1

14. Why is digester gas corrosive?

Because CO2mixes with water to form HCO

3(carbolic acid)

15. What causes the scum layer in a digester?

The uplifting of material by the gas

16. Water (supernatant) in a digest may come from:

a. carrier water

b. water from killed bacterial cells

17. Digester supernatant can have a BOD of1000

a SS of 5000 to 15,000 mg/L.

to10,000 mg/L and

18. What are the characteristics of good quality digester sludge?

Black, no green or gray streaksDewaters easilyNo noxious odors40-60% lower V.S. than feed

I-AND-27

3 5

ANAEROBIC DIGESTION

Worksheet 2 - Types and Components

1. Identify the following digesters by cover' type (fixed, floating or gas holding).

a fixedb. oasholdinoc. floating

A.

B

.1

I

*-".

64,

-11.(141,1, .; --. it

I-AND- 28

36

2. Identify the components of the digester gas system indicated.

I4 4Cm0 W4

?2zo

(1)4J C9

OCW0

z

Wz C94 ES

W0LL a-

4 IE. 2

I-AND-29

3 7

a. flame arrestor

b. thief hole

c. roof level indicator

d. moisture trap

e. heat sensitive valves

f. sediment trap

g. manometer (pressure gauge)

h. pressure regulator

waste gas burner

j. gas meter

3. The roof of a fixed roof digester may be made of steel

concrete

or

4. Internal pressure of a fixed roof digester should not exceed 8

inches of water.

5. Digester heat exchangers may be either internal or external

6. Digester sludge may be mixed with digester gas , mechanical mixed

or with combinations .

7. Internal pressure on a floating roof digester should be between

and 11 inches of H2O.

8. Name the three temperature zones used to classify digesters.

a. Psychrophilic

b.

c.

Mesophilic

Thermophilic

9. Why is it necessary to have commercial natural gas on hand?

For emergency and start up use.

10. Name two types of sludge pumps.

piston pumps

"Moyno" type pumps

"hose" pumps

centrifugal

I-AND-30

8

ANAEROBIC DIGESTION

Answers to Worksheet 3 Operational Control

1. Name 6 factors which affect digester operation.

a. bacteria

b. food

c. loading

d. mixing

e. temperature

f. pH

toxics

2. There should be 20 times for seed sludge (bActeria) than food by

weight of volatile matter.

3. List 3 characteristics of good quality feed sludge.

a. 5-8% solids

b. non-toxic

c. stable pH

feed at steady rate and frequency

4. Give the normal operating ranges for each of the following:

VA/Alk ratio

V.S./ft3 loading

temperature

less than 0.25

0.03 - 0.1

95 - 98°F

pH 6.8 7.2

feed sludge conc. 5 8%

5. How does hydraulic loading affect detention time?

Higher flows decrei...e detention time

6. How is the optimum operating temperature determined?

By optimizing CO2 production at 30% or lower

7. Digester temperature should be changed no more than 1 °F/day.

8. Volatile acid concentrations in the digester can fall in the range of

50 to 300 mg/L.

I-AND-31

9. Alkalinity in the digester can fall in the range of 3000 to 6000

mg/L.

10. How is detention time controlled?

By adjusting feeding and withdrawal pumping rates.

11. If digester supernatant BOD and SS concentration exceeds 5000 mg/L,

the biological system of the plant may become overloaded.

12. List the 5 sample points of a typical digester.

a. Raw feed

b. Supernatant

c. Gas

d. Digested Sludge

e. Dijesting Sludge

13. For the following tests indicate the samples upon which they shbuld be run:

pH and temperature

Feed, Supernatant, Digested Sludge, Digesting Sludge

Flow -

Feed, Digested Sludge, Digesting Sludge

Solids (Total, Volatile & % Moisture)

Feed, Supernatant, Digested Sludge, Digesting Sludge

CO2

Gas

BOD & SS

Supernatant

Volatile Acids & Alkalinity -

Digesting Sludge

I-AND-32

ANAEROBIC DIGESTION

Answers to Worksheet 4 - Calculations

Consider the following data for an anaerobic digester.

Raw Digested Supernatant

Quantity 12,000 gal/day 12,000 gal/day

Total Solids, mg/L 40,000 mg/L (4%) 60,000 mg/L 4,000 mg/L

Vulatile Solids (% of T.S.) 70% 45% 60%

Digester Volume 250,000 gal (33,400 ft")

Digesting Sludge 2% (20,000 mg/L)

1. Calculate pounds T.S. in digester.

T.S., lhs = T.S., mg/L X Vol, MGal X 8.34

= 20,000 X 0.25 X 8.34

= 41,700 lbs

2. Calculate pounds T.S. in raw feed sludge.

T.S., cos /day = T.S., mj/L X Flow, MGa1 /day X 8.34

= 40,000 X 0.012 X 8.34

= 4000 lbs/day

3. Calculate pounds T.S. in supernatant

T.S., lbs/day = T.S., mg/L X Flow, MGa1 /day X 8.34

= 4000 X 0.01', X 8.34

= 400 lbs/day

4. Calculate Hydraulic Detention Time.

Hyd. Det. Time, daysVol, gal

Raw feed, gal /day

250,000 ger

12,000 gall /day

20.8 days

5. Calculate pounds Vc'atile Solids fed.

V.S., lbs/day = T.S., lbs/day X % Volatile

4000 X 0.7

2800 lbs/day

6. Calculate volatile solids loading in lbs/day/ft3.

Loading, lbs/day/ft3 = V.S., lbs/day

Dig. Vol., ft3

2800 lbs/day

33,400 ft3--

= 0.083 lbs/day/ft3

7. Calculate volatile solids loading in lbs V.S./day per lb V.S. in digester.

Loading lbs/day/lb =V.S., lbs/day

V.S. in Dig, lbs

2800 lbs/day

41,700 lb X 0.45

= 0,15 lbs/day/lb

I-AND-34

8. Calculate Volatile Solids Reduction.

in V.S. outV.S. reduction, %

V.S.= X 100%

V.S. in (V.S. in X V.S. out)

.70 - .45 X 100%

.70 - (.70 X .45)

.25 X 100%

.38

= 66%

9. Calculate pounds of volatile solids digested.

V.S. digested, lbs/day/ft3 = Loading, lbs/day/ft3 X V.S. Reduction %

= 0.083 X 0.66%

= 0.055 lbs/day/ft3

10. A digester has a volume of 250,000 gal. Lab tests show that 0.075 lbsof lime is necessary to bring the pH of a 5 gal sample up to 6.8. Howmany lbs of lime are necessary to adjust the pH of the entire digester?

5 gal

0.15 lbs

X lbs

250,000 gals

X lbs

250,000 gal X 0.075 lbs

5 gal

3750 lbs

11. If a digester of Vol. 250,000 gal has 2000 mg/L of Volatile Acids, howmany lbs of lime will be needed to neutralize the V.A.'s?

lbs = Vol, Mgal X V.A., mg/L X 8.34

= 0.250 X 2000 X 8.3e

= 4170 lbs

I-AND-35 43

12. If a digester of Vol. 250,000 gal, the alkalinity is 2000 mg/L and thevolatile acids is 3500 mg/L, how many lbs of 80% anhydrous ammonia areneeded to neutralize the V.A.'s? (Assume an excess of 500 mg/Lalkalinity needed.)

Alk. needed to neutralize VA = 0.833 X VA

- 0.833 X 3500

= 2915 mg/L

Need to Add Alk. = 2915 - 2000

= 915 mg/L

To have 500 mg/L excess = 915 + 500

. 1415 mg/L

Ammonia, lbs = 2.78 X Dig. Vol, Mgal X Alk needed mg/L

= 2.78 X 0.25 X 1415

983.4

Anhydrous NH4, lb = 983.4

0.8

= 1229 lbs

1-AND-36

ANAERBOIC DIGESTION

Final 'quiz

1. Match the letters on the diagram with their description:

gas collection and removal system

boiler

mixing

tank

heat exchanger

2. Which of the following are considered valid purposes of anaerobicdigestion? (select five)

a. reduce water consumption

b. increase volatile content

c. reduce volatile content

d. reduce odor

e. prevent reliquification

f. produce usable gas

g. reduce mass of sludge

h. condition sludoe

i. improve plant efficiency

j. reduce numbers of pathogenic organisms

3. The volatility of sludge is an indication of:

a. heat production capabilities.

b. sludge food value.

c. weight of the sludge.

d. the difference between the weight of the sludge and the weightof an equal volume of water.

e. all of the above.

4. Anaerobic digestion is basically a step process.

a. 4

b. 3

c. 2

d. 6

e. none of the above

5. The first stage of digestion converts

a. volatile solids to methane

b. methane to acid formers

c. volatile acid to methane and CO2

d. volatile solids to volatile acids


46

1-AND-38

6. During the second stage of digestion there is a conversion of:

a. volatile acids to pH.

b. volatile acids to methane.

c. volatile solids to volatile acids.

d. microorganisms to food.


7. During the second stage of digestion a buffering material is produced.This buffering material is usually called:

a. alkalinity.

b. CO2.

c. pH.

d. acid,

e. none of the above.

8. The most acceptable pH range for anaerobic digestion is between:

a. 6.5 and 7.5

b. 6.4 and 8.4

c. 6.8 and 7.2

d. 5 and 8


9. When a digester contains such items as petroleum products, plastic,rubber goods and etc., these materials may form a layer on the top ofa digester. This layer is usually called:

a. upper layer.

b. supernatant.

c. scrapings.

d. scum blanket.


10. The BAD range for digester supernatant would probably run between:

a. 2,500 and 1,000,000 lbs/day,

b. 1,000 and 100,000 mg/kg.

c. 10,000 and 100,000 mg/l.

d. 1,000 and 10,000 mg/l.


4 7

I-AND-39

11. Supernatant from an anaerobic digester could have a S.S. level oetween:

a. 5,000 and 15,000 mg/l.

b. 500 and 1,500 mg/l.

c. 500 and 1,500 kg/g.

d. 500 and 15,000 kg/l.


12. A description of properly digested sludge might be:

a. green and contain black and gray streaks.

b. gray and contain streaks of black and dark green.

c. black and contain no green or gray streaks.

d. black and contain a few green or gray streaks.


13. The volatility of properly digested sludge should be reduced by:

a. 20 40%.

b. 40 - 60%.

c. 60 - 80%.

d. 50 - 70%.

e. none of these.

14. If the digester is operated properly, the gas production will usually

contain methane at:

a. 65 70%.

b. 40 - 65%.

c. 30 - 40%.

d. 70 80%.

e. none of these.

15. For each 1 pound of volatile material that is reduced by digestion gas

is produced. The approximate volume produced for each pound would be:

a. 12 - 18 mg/l.

b. 12 - 18 kg.

c. 12 18 cubic yards.

d. 12 - 18 cubic feet.


48I-AND-40

16. DisJstion may be classified by function. On the list below, place

an "X" beside the three terms used to describe these three ;unctions:

a. digestion

b. primary

c. solids reduction

d. conditioning

e. secondar:

f. gas production

g. energy cost savings

h. gas producers

i. gas holding

17. Select the proper name for the most common digester operating range.

a. mesophilic

b. psychrophilic

c. esophilic

d. thermophilic


18. Select the temperature range for the most common digester operatingrange.

a. 65-78° F

b. 79-95° F

c. 95-98° F

d. 98-108° F


19. For a normally operated anaerobic digester operating within the typicaltemperature range, complete sludge digestion should take place in:

a. 10-20 days

b. 20-30 days

c. 30-35 days

d. 40-50 days


20. In order to maintain an anaerobic digester in optimum condition, thedigester sludge temperature should not change more than

degrees F. per day.

a. 4

b. 3

c. 2

d. 1


21. From the list below, select the three most common types of heat exchangers.

a. internal combustion engine

b. direct gas flame

c. low pressure

d. coil type

e. internal

f. draft tube

g. external

h. boiler

22. The major purpose for mixing is to: (select one)

a. bring food and microorganisms into contact.

b. break up the scum blanket.

c. reduce energy requirements by circulating heated sludge.

d. release gas from the sludge particles.

23. The most common volatile acids to alkalinity ratio for an anaerobicdigester would be:

a. > 0.25

b. > 150

c. 0.4

d. < 0.25

e. < 0.4

24. Using the diagram below, indicate what material is being sampled at

each point.

supernatant

raw sludge

digesting sludge

gas

digested sludge

%..ii::11=...

25. Typical volatile solids/ft3loadings for an anaerobic digester

might be:

a. 0.004 to 0.04 lbs/ft3

b. 0.04 to 0.4 lbs/ft3

c. 0.03 to 0.1 lbs/ft3

d. 0.03 to 1.0 lbs/ft3


26. Using the drawing above, match the items indicated with the description.

flame arrester

waste gas burner

gas meter

heat sensitive valve

moisture and sediment traps

manometers

I-ANL-44

52

27. Calculate hydraulic detention time if the digester contains 185,000

gal and the feed rate is 9500 galiday.

a. 17.6 hrs

b. 19.5 days

c. 20.3 days

d. 19.5 min.

28. Calculate pounds of in feed Fwr day if the T.S. is 3.6% (36,000 mg/L),the % volatility is 68% and the feed rate is 9500 gal /day..

a. 1940 lbs/day

b. 615 lbs/day

c. 2050 lbs/day

d. 5130 lbs/dey

29. Calculate loading in lbsisy/ft3for the plant described in Problems

27 and 28.

a. 0.15 lbs/day/ft3

b. 0.019 lbs/day/ft3

c. 0.078 lbs/day/ft3

d. 0.553 lbs/day/ft3

I-AND-45

30. Calculate % volatile solids reduction if the V.S. of the feed is

68% and the V.S. of the digested sludge is 40%.

a. 45%

b. 51%

c. 62%

d. 68%

1-AND-46

54

ANAERBOIC DIGESTION

Answers to Final Quiz

1. Match the letters on the diagram jth their description:

E gas collection and removal system

C boiler

A mixing

B tank

D heat exchanger

2. Which of the following are considered valid purposes of anaerobic

digestion? (select five)

a. reduce water consumption

b. increase volatile content

X c. reduce volatile content

x d. reduce odor

e. prevent reliquification

f. produce usable gas

x g. reduce mass of sludge

X h. condition sludge

i. improve plant efficiency

X j. reduce numbers of pathogenic organisms

3. The volatility of sludge is an indication of:

a. heat production capabilities.

X b. sludge food value.

c. weight of the sludge.

d. the difference between the weight of the sludge and the weightof an equal volume of water.


4. Anaerobic digestion is basically a step process.

a. 4

b. 3

X c. 2

d. 6


5. The first stage of digestion converts

a. volatile solids to methane

b. methane to acid formers

c. volatile acid to methane and CO2

d. volatile solids to volatile acids


to

6. During the second stage of digestion there is a conversion of:

a. volatile acids to pH.

X b. volatile acids to methane.

c. volatile solids to volatile acids.

d. microorganisms to food.


7. During the second stage of digestion a buffering material is produced.This buffering material is usually called:

X a. alkalinity.

b. CO2.

c. pH.

d. acid.


8. The most acceptable pH range for anaerobic digestion is between:

a. 6.5 and 7.5

b. 6.4 and 8.4

X c. 6.8 and 7.2

d. 5 and 8


9. When a digester contains such items as petroleum products, plastic,rubber goods and etc., these materials may form a layer on the top of

a digester. This layer is usually called:

a. upper layer.

b. supernatant.

c. scrapings.

X . scum blanket.


10. The BOD range for digester supernatant would probably run between:

a. 2,500 and 1,000,000 lbs/day.

b. 1,000 and 100,000 mg/kg.

c. 10,000 and 100,000 mg/l.

X d. 1,000 and 10,000 mg/l.


11. Supernatant from an anaerobic digester could have a S.S. level between:

X a. 0,000 and 15,000 mg/l.

b. 500 and 1,500 mg/l.

c. 500 and 1,500 kg/g.

d. 500 and 15,000 kg/l.


12. A description of properly digested sludge might be:

a. green and contain black and gray streaks.

b. gray and contain streaks of black and dark green.

X c. black and contain no green or gray streaks.

d. black and contain a few green or gray streaks.


13. The volatility of properly digested sludge should be reduced by:

a. 20 - 40%.

X b. 40 - 60%.

c. 60 - 80%.

d. 50 - 70%.

e. none of these.

14. If the digester is operated properly, the gas production will usually

contain methane at:

X a. 65 70%.

b. 40 - 65%.

c. 30 40%.

d. 70 - 80%.

e. none of these.

15. For each 1 pound of volatile material that is reduced by digestion gas

is produced. The approximate volume produced for each pound would be:

a. 12 - 18 mg/1.

b. 12 - 18 kg.

c. 12 18 cubic yards.

X d. 12 - 18 cubic feet.


I-AND-50

56

16. bigestion may be classified by function. On the list below, placean "X" beside the three terms used to describe these three functions:

a. digestion

b. primary

c. solids reduction

d. conditioning

X e. secondary

f. gas production

g. energy cost savings

h. gas producers

X i. gas holding

17. Select the proper name for the most common digester operating range.

X a. mesophilic

b. psychrophilic

c. esophilic

d. thermophilic


18. Select the temperature range for the most common digester operatingrange.

a. 65-78° F

b. 79-95° F

X c. 95-98° F

d. 98-108° F


19. For a normally operated anaerobic digester operating within the typicaltemperature range, complete sludge digestion should take place in:

a. 10-20 days

X b. 20-30 days

c. 30-35 days

d. 40-50 days


I-AND-51

59

20. In order to maintain an anaerobic digester in optimum condition, the

digester sludge temperature should not change more than

degrees F. per day.

a. 4

b. 3

c. 2

X d. 1


21. From the list below, select the three most common types of heat exchangers.

a. internal combustion engine

X b. direct gas flame

c. low pressure

d. coil type

X e. internal

f. draft tube

x g. external

h. boiler

22. The major purpose for mixing is to: (select one)

X a. bring food and microorganisms into contact.

b. break up the scum blanket.

c. reduce energy requirements by circulating heated sludge.

d. release gas from the sludge particles.

23. The most common volatile acids to alkalinity ratio for an anaerobic

digester would be:

X

a. > 0.25

b. > 150

c. 0.4

d. < 0.25

e. < 0.4

1-AND-52

60

24. Using the diagram below, indicate what material is being sampled at

each pojnt.

0 supernatant

A raw sludge

C digesting sludge

B gas

E digested sludge

,...=11

I-ANO-53

61

25. Typical volatile solids/ft3 loadings for an anaerobic digestar

might be:

a. 0.004 to 0.04 lbs/ft3

b. 0.04 to 0.4 lbs/ft3

X c. 0.03 to 0.1 lbs/ft3

d. 0.03 to 1.0 lbs/ft3


26. Using the drawing above, match the items indicated with the description.

A flame arrester

F waste gas burner

E gas meter

0 heat sensitive valve

moisture and sediment traps

manometers

I-AND-54

62

27. Calculate hydraulic detention time if the digester contains 185,000gal and the feed rate is 9500 gal/day.

X

a. 17.6 hrs

b. 19.5 days

c. 20.3 days

d. 19.5 min.

Hyd. Det. Time, days =Vol, gal

Feed Rate, gal/day

185,0009501

= 19.5 days

28. Calculate pounds of V.S. in feed per day if the T.S. is 3.6% (36,000 mg/L),the % volatility is 68% and the feed rate is 9500 gal/day.

X a. 1940 lbs/day

b. 615 lbs/day

c. 2050 lbs/day

d. 5130 lbs/day

V.S., lbs/day = T.S. mg/L X Flow, Mgal/day X 8.34 X % Volatility

= 36000 X 0.0095 X 8.34 X 0.68

= 1940 lbs/day

29. Calculate loading in lbs/day/ft3

for the plant described in Problems27 and 28.

a. 0.15 lbs/day/ft3

Loading, lbs /day /ft3 = $.

3 V.S., lbs/day

b. 0.019 lbs/day/ft3 Dig. Vol, ft''

X c. 0.078 lbs/day/ft31940 lbs/day

d. 0.553 lbs/dayift3

ft 3

I-AND-55

63

185,000 gal X7.48 Ile

= 0.078 lbs/day/ft3

30. Calculate % volatile solids reduction if the V.S. of the feed is

68% and the V.S. of the digested sludge is 40%.

a. 45%

b. 51%

c. 62%

X d. 68%

V.S. Reduction, % =V.S. in - V.S. out

V.S. in - (V.S. in X V.S. out)

U.68 0.40

0.68 (0.68 X 0.40)

= 68%

1-AND-56

64

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